Sony Playstation Controller Port
9 PIN UNKNOWN CONNECTOR
1 2 3 4 5 6 7 8 9 ------------------------------- | o o o | o o o | o o o | (at the Controller) \_____________________________/
Signal from Controller to PSX. This signal is an 8 bit serial transmission synchronous to the falling edge of clock (That is both the incoming and outgoing signals change on a high to low transition of clock. All the reading of signals is done on the leading edge to allow settling time.)
Signal from PSX to Controller. This signal is the counter part of DATA. It is again an 8 bit serial transmission on the falling edge of clock.
VCC can vary from 5V down to 3V and the official SONY Controllers will still operate. The controllers outlined here really want 5V. The main board in the PSX also has a surface mount 750mA fuse that will blow if you try to draw to much current through the plug (750mA is for both left, right and memory cards).
ATT is used to get the attention of the controller. This signal will go low for the duration of a transmission. I have also seen this pin called Select, DTR and Command.
Signal from PSX to Controller. Used to keep units in sync.
Acknowledge signal from Controller to PSX. This signal should go low for at least one clock period after each 8 bits are sent and ATT is still held low. If the ACK signal does not go low within about 60 us the PSX will then start interogating other devices.